Body armor has been around for a long time. In general, the desire is to make the body armor as light and as breathable as possible and still withstand the impact of incoming projectiles. In recent years, some body armor has been made from a woven and/or a non-woven fabric comprising filaments of very high molecular weight polymers, suitably polyolefin, such as polyethylene or high molecular weight polypropylene, and aramid polymers. Reference is here made to U.S. Pat. No. 4,737,402 in the name of Harpell et al. which has an excellent discussion of the chemical nature of these filaments which have been found to be well suited to use in protective fabrics. The entire contents of this patent are hereby incorporated herein by reference. The object of these fabrics is to cause the incoming ballistic projectile to expend its energy breaking the filaments of the fabric, and therefore lose its impetus to penetrate into the body being protected by the fabric.
It had recently been found, see U.S. Pat. No. 5,395,671, the entire substance of which is incorporated herein by reference, that a certain construction of a composite fabric, comprising multi-layers of high molecular weight woven and non-woven fabrics assembled in a particular manner, had unusual ability to stop the penetration of even very high energy projectiles, such as a very high energy projectile issuing from a 0.44 magnum bullet. This fabric comprised two independent layers of material. That is the two layers of material, each composed of a plurality of sub-layers, were not attached to each other. The side of the fabric facing in the direction from which the projectile is incoming is suitably made of multiple sub-layers or plies of non-woven fabric, comprising very high molecular weight polymer filaments. The side of the fabric disposed away from the incoming direction of the projectile, and toward the object in need of protection, is suitably made up of multiple sub-layers or plies of woven fabric, comprising high molecular weight polymer filaments, which woven sub-layers or plies have been quilted together. The fact that only the sub-layers or plies of the woven fabric are quilted together and the fact that the plies of non-woven fabric are disposed toward the incoming projectile are essential criteria of the invention of the '671 patent because it is the combination of these two elements which causes the finished composite fabric to have its unusual and unexpectedly effective stopping power.
Another recent development in this field is disclosed in U.S. Pat. No. 5,343,796. This patent describes a composite fabric protective system comprising an outer, or face, layer which has as its purpose to slow the velocity of the incoming projectile so that the second, underlayer, then can stop this now lower velocity projectile. According to this patent, the first, or face, layer is a pliable, cut resistant fibrous layer; and the second, or inside, layer is a pliable impact/ballistic energy absorbing fibrous layer. The '796 patent also alleges that the first and second layers can be reversed with the energy absorbing layer being the face layer and the cut resistant layer being the second layer. Three layer systems are also disclosed where the third layer is like the first layer.
Many different fibers and fiber combinations are disclosed in this reference and the entirety of this reference is therefore incorporated herein by reference. Any of these fibers and fiber combinations can be used in the practice of the instant invention.
The composite fabric of the '671 patent is an excellent protective material from which excellent protective garments are made. However, because this composite fabric was intended to stop a 240 grain 0.44 magnum bullet traveling at an impact velocity of 1450 feet per second, the fabric is necessarily fairly thick. It is made up many layers of both woven and non-woven sub-layers which have been assembled as aforesaid. Because this fabric has to have this exceptional stopping power, it is thus necessarily made up of these multiple layers of woven and non-woven fabrics. The requirement of this fabric that it stop a 0.44 magnum projectile, requires that there be a substantial number of layers of non-woven fabric in this composite. The use of such multiple layers of non-woven fabrics, made of high molecular weight polymer filaments, makes the fabric reasonably stiff and therefore less than ultimately comfortable to the wearer.
Despite the need for serious impact protection which is answered by the fabric of the '671 patent, this special fabric structure has been assembled at a rather low areal density of about 0.95 to 1.15 pounds per square foot. It has been found that with this special structure, it is possible to make up this composite fabric in such a low areal density and still stop a projectile from a 0.44 magnum bullet traveling at an impact velocity of 1,450 feet per second. This was most unusual at the time of its invention and has found some commercial success for body armor offering Level IIIA protection.
Stiff protective clothing, particularly such clothing which has a very tight weave or disposition of filaments, and even more particularly such clothing which comprises layers of non-woven fabric, has a degree of discomfort to the wearer in direct proportion to its areal density and its flexibility. For the same polymer filaments, it is axiomatic that the higher the areal density of the fabric, the greater is the stopping power of the fabric. It is also a fact that, for fabrics made up of the same filaments, the higher the areal density of a fabric, the stiffer it is because it has progressively fewer void spaces.
In modern protective clothing, a balance must be struck between the stopping power of the garment or fabric and the degree of discomfort the wearer is willing to put up with. If the fabric has too few filaments, or if the molecular weight and denier of the filaments making up the fabric is too low, or if the fabric is too thin, there will be insufficient protection afforded the wearer, and the fabric will not have achieved its purpose. The direction in which this art is going is consistent with the direction in which the power of guns is going. That is, with time, the impact velocity and penetrating power of ballistic projectiles has continued to increase, and therefore, the stopping power of protective garments has also increased. This has been accomplished by using stronger and higher molecular weight filaments, by increasing the weight and stiffness of the fabric, and by assembling the fabric from different elements, such as both woven and non-woven fabrics, which provide different, and cumulatively superiorly effective, kinds of stopping power. However, it is desired to lighten the fabric and make it less uncomfortable to the wearer, and still have it stop incoming ballistic projectiles.